Optical Lever Measurement Accuracy for Off-Resonance Atomic Force Microscopy
Author
Eason, Richard Parker
Date
2011Advisor
Dick, Andrew J.
Degree
Master of Science
Abstract
This research evaluates measurement accuracy in optical lever-based atomic force
microscopy (AFM) for off-resonance conditions and parameter variations. Under controlled
conditions and correct calibration, AFM provides researchers with the ability
to accurately observe and manipulate matter on the micro- and nano-scale. Accuracy
of imaging and nano-manipulation operations are directly correlated to the
accuracy with which the displacement of the probe is measured. The optical lever
method, a common displacement measurement technique employed in AFM, calculates
probe displacement based on a calibration that assumes a consistent response
profile throughout operation. Off-resonance excitation and tip-sample interaction
forces during intermittent contact mode AFM can alter this response profile. Standard
tapping-mode operation at the fundamental frequency is observed to be robust
to changes in effective stiffness, maintaining accurate measurements for all laser spot
positions considered. A nominal laser spot position between Xp = 0.5 and 0.6 is determined
to most accurately predict displacement for off-resonance excitation during
both free response and intermittent contact condit ions. Measurement accuracy for
off-resonance tapping- mode is more directly correlated to changes introduced to the
interaction force profile than choice of spot position.
Keyword
Mechanical engineering; Materials science